(1) Field of the Invention
This invention relates to the use of fracture patterns and pattern fracturing rules to fabricate masks having optical proximity correction.
(2) Description of the Related Art
The usual pattern fracturing rule for electron beam exposure patterns is to fracture the pattern along one direction, horizontal or vertical direction. When masks having optical proximity correction are fabricated using vector scan electron beam writers these pattern fracturing rules can cause problems, such as resist scum residue, at pattern jogs required for optical proximity correction. Multiple fracture elements perpendicular to the edge of a critical dimension line will also cause problems, such as resist scum residue.
U.S. Pat. No. 5,858,591 to Lin et al. describes a method for optical proximity correction. The method splits the full description data file into two subfiles, one subfile where the density of lines is high and one subfile where the lines tend to be isolated. A bias is then applied to the subfiles and the subfiles are merged back into a single data file.
U.S. Pat. No. 5,862,058 to Samuels et al. describe a method of optical proximity correction that allows for correction of line width deviations.
U.S. Pat. No. 5,847,421 to Yamaguchi describes a method of optical proximity correction using a basic cell library.
U.S. Pat. No. 5,553,273 to Liebman describes an optical proximity correction method which predistorts the mask while biasing only critical features and eliminating, as much as possible, the creation of additional vertices.
When masks having patterns with optical proximity correction, OPC, are fabricated pattern fracturing is often used. The pattern fracturing segments the pattern into a number of rectangular elements which can be reproduced with an electron beam pattern writer. The usual pattern fracturing rule for electron beam exposure patterns is to fracture the pattern along one direction, horizontal or vertical, as shown in FIGS. 1 and 2. This pattern fracturing rule can cause problems for vector scan electron beam writers. The vector scan electron beam writers are frequently used because they have higher throughput than other types of electron beam writers.
The vector scan electron beam writer system is shown schematically in FIG. 3. In the vector scan electron beam writer an electron beam 40 passes through a number of apertures, 36 and 38, to form a pattern on a layer of positive resist 34. The layer of positive resist 34 is formed on a layer of opaque material 32, such as chrome. The layer of opaque material 32 is formed on a transparent mask substrate 30.
FIGS. 1 and 2 show pattern fracture rules which cause problems in the fabrication of masks with the vector scan electron beam writer. In FIGS. 1 and 2 the pattern elements are cross hatched to make them more visible while the fracture elements are not cross hatched. FIG. 1 shows a fracture pattern of a pattern element 10 formed by rectangular fracture elements oriented in the same direction as the pattern element 10, in this example horizontal. A pattern jog 11 is required by optical proximity correction and this jog 11 will result in fracture elements 12 having a very small width 14. When masks are fabricated with the pattern shown in FIG. 1 using the vector scan electron beam writer resist scum will remain at the edge of the pattern element 10 in the narrow rectangle 12 adjacent to the pattern element.
FIG. 2 shows a pattern having pattern elements 22, 23, and 25 perpendicular to the fracture elements. In this example the pattern elements 22, 23, and 25 are vertical and the fracture elements are horizontal. This pattern layout and fracturing rules will cause fracture element ends 28 to contact part of the sides of the pattern elements 22, 23, and 25. These fracture element ends 28 will cause resist residue.
It is a principle objective of this invention to provide a method of forming a mask pattern using fracture elements which avoids the formation of resist residue.
It is another principle objective of this invention to provide a method of forming a mask using a mask pattern having fracture elements and a vector scan electron beam writer which avoids the formation of resist residue.
These objectives are achieved by the use of new pattern fracture rules. In these new pattern fracture rules special fracture elements are used along each side of the pattern elements. These special fracture elements are used for pattern elements parallel to and perpendicular to the fracture elements. The use of these special fracture elements prevent fracture element ends from contacting the sides of the pattern elements and avoids the formation of resist residue at the pattern edges.